1. Field of the Invention
This invention relates to packaging of semiconductor integrated circuits, and more particularly to apparatus and method including the use of lead frames in place of substrates for mounting solder balls of ball grid array packages.
2. Description of the Related Art
Ball grid array packaging of semiconductor integrated circuits uses an array of solder balls on the bottom of the package as leads for connection of the semiconductor integrated circuit (IC) to external components. An array of solder balls on the bottom surface of the package results in higher density packaging and are easier to use since they can be more widely separated.
Currently, ball grid array packages are constructed with the semiconductor die mounted on one face of a substrate, and the solder balls mounted on the opposite face of the substrate. Circuitry on the substrate provides the necessary interconnection between the die and solder balls. Substrates are currently made of either ceramic, printed circuit board (PCB) lamninate, or flexible, plastic tape.
Ceramic substrates in ball grid array packaging typically suffer from reliability problems when mounted to PCB mother boards due to a thermal expansion mismatch of the ceramic and the PCB. Also, for either ceramic, PCB laminate, or tape substrates, only one surface has solder balls, so the packages cannot be conveniently stacked. Thus, current ball grid array packaging does not provide for increased package mounting density and less board space usage which results from stacking packages.